In modern motor vehicles, in particular passenger cars, automated clutches, such as those described in DE 10 2011 014 936 A1, are being used to an increasing degree. The use of such clutches has the benefit of improved driving comfort, and has the result that it is more often possible to drive in gears with a high gear ratio. The clutches used here are utilized in hydraulic clutch systems, in which an electrohydraulic actuator, which is driven by an electrically commutated motor, is connected to the clutch by means of a hydraulic line.
In particular with electric motors in which the sensors are situated outside the axis of rotation of the electric motor, high position resolution is necessary. In this case, a magnetic transmitter ring is non-rotatably connected to the rotor of the electric motor, for example on a shaft end (on-axis), while the sensor system that senses the magnetic transmitter ring is attached, for example, to the stator (off-axis). The position of the sensor system does not change. The rotor of the electric motor has a limited number of pairs of poles, from which a specified number of flanks of the magnetic field switch are used to determine the position.
It is known that with small diameters of the magnetic transmitter ring situated on the rotor, in practice a two-pole magnet is used as the circular ring, which enables the position of the rotor to be reliably resolved electrically to 360° by the analysis unit. With regard to the diameter of the magnetic transmitter ring, it is limited however, since the curvature of the magnetic field over the pair of poles is not always adequate to obtain sufficient resolution of the sensor signal picked up by the sensors.
The use of multiple sensors is also known, for example with 5 sensors (3 switching Hall sensors and 2 analog Hall sensors) being used in practice. This requires considerable construction space in the clutch, however, and is an expensive solution.
Thus there exists a long felt need for a method for determining and controlling a position of an electric motor in a clutch actuation system of a motor vehicle wherein the position of a rotor of the electric motor is picked up by a sensor system situated on a stator of the electric motor outside an axis of rotation of the electric motor.